Bipolar Resistive Memory Research Articles

Characteristics of HfO2/Hf-based bipolar resistive memories**Project supported by the National Natural Science Foundation of China (Nos. 11179003, 61176095).

Nano-scale Hf/HfO2-based resistive random-access-memory (RRAM) devices were fabricated. The cross-over between top and bottom electrodes of RRAM forms the metal–insulator–metal sandwich structure. The electrical responses of RRAM are studied in detail, including forming process, SET process and RESET process. The correlations between SET voltage and RESET voltage, high resistance state and low resistance state are discussed. The electrical characteristics of RRAM are in a strong relationship with the compliance current in the SET process. The conduction mechanism of nano-scale Hf/HfO2-based RRAM can be explained by the quantum point contact model.

Thickness effect on the bipolar switching mechanism for nonvolatile resistive memory devices based on CeO2 thin films

Impact of switching layer thickness on the bipolar resistive memory performance, stability and uniformity has been investigated in Ti/CeO2/Pt devices. XRD and FTIR analyses demonstrate polycrystalline nature of CeO2 films and the formation of a TiO interface layer. The bipolar switching characteristics like HRS and LRS dispersion are found to be dependent on the thickness of CeO2 layer. As it is noted that forming as well as SET voltages gradually increase with increasing CeO2 layer thickness however RESET voltages are slightly affected. Oxygen gettering ability of Ti causes the formation of TiO layer, which not only extracts oxygen ions from the ceria film but also acts as ion reservoir, hence plays a key role in stable functioning of the memory devices. Current transport behavior is based upon Ohmic and interface modified space charge limited conduction. Based on unique distribution characteristics of oxygen vacancies in CeO2 films, a possible mechanism of resistive switching in CeO2 RRAM devices has been discussed.

Composition-Ratio Influence on Resistive Switching Behavior of Solution-Processed InGaZnO-Based Thin-Film

The influence of composition ratio on the bipolar resistive switching behavior of resistive switching memory devices based on amorphous indium-gallium-zinc-oxide (a-IGZO) using the spin-coating process was investigated. To study the stoichiometric effects of the a-IGZO films on device characteristics, four devices with In/Ga/Zn stoichiometries of 1:1:1, 3:1:1, 1:3:1, and 1:1:3 were fabricated and characterized. The 3:1:1 film showed an ohmic behavior and the 1:1:3 film showed a rectifying switching behavior. The current-voltage characteristics of the a-IGZO films with stoichiometries of 1:1:1 and 1:3:1, however, showed a bipolar resistive memory switching behavior. We found that the three-fold increase in the gallium content ratio reduces the reset voltage from -0.9 to - 0.4 V and enhances the current ratio of high to low resistive states from 0.7 x 10(1) to 3 x 10(1). Our results show that the increase in the Ga composition ratio in the a-IGZO-based ReRAM cells effectively improves the device performance and reliability by increasing the initial defect density in the a-IGZO films.

Interrelation of Sweep and Pulse Analysis of the SET Process in SrTiO<sub>3</sub> Resistive Switching Memories

In this letter, we present a study of the SET kinetics of bipolar switching SrTiO 3 -based resistive memory devices. Pulse measurements on a timescale from 1 μs to 1 s and voltage sweeps with sweep-rates up to 6 MV/s were performed showing a highly nonlinear correlation between voltage and time. An analytical model is presented that explains the interrelation of both experiments by a comparative analysis of the current- voltage characteristics.

Analytical Modeling of Oxide-Based Bipolar Resistive Memories and Complementary Resistive Switches

To allow for novel memory and computing schemes based on the resistive switching memory (RRAM), physically based compact models are needed. This paper presents a new analytical model for HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -based RRAM, relying on a simplified description of the conductive filament (CF) in terms of its diameter and gap length. The set and reset operations are described by CF growth and gap opening, respectively, activated by the local field and temperature. The analytical model is then used to describe the switching dynamics in the complementary resistive switch (CRS), consisting of an antiserial connection of two resistive devices. The impact of the gap resistivity on the CRS characteristics is discussed, highlighting the tradeoff between off-state leakage and set/reset window.

Non-volatile, electric control of magnetism in Mn-substituted ZnO

We show that the magnetic properties of a dilute semiconductor oxide can be altered in a reversible and non-volatile manner by the application of an electric field. The selected ferromagnetic oxide was manganese-substituted zinc oxide. Bipolar resistive memory switching was induced in the film sandwiched between two metallic electrodes. The bistable switching of the resistive state was accompanied by a bistable switching of the magnetic moment. The scalability of the system was investigated by fabricating devices with lateral size down to 400 nm.

The Impact of X-Ray and Proton Irradiation on ${\rm HfO}_2/{\rm Hf}$-Based Bipolar Resistive Memories

This paper investigates total-ionizing dose effects on the electrical characteristics of HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Hf-based bipolar resistive-random-access-memory (RRAM) devices. 10-keV x-ray irradiation does not cause significant changes in resistance at levels up to 7 Mrad( SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). Excess carriers generated by x-ray irradiation in the HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer recombine or are trapped at defect sites in the HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer or at interfaces between layers. They have no effect, however, on the conductive path of the RRAM devices. 1.8 MeV proton irradiation causes resistance degradation through simultaneous introduction of oxygen vacancies and displacement damage. TRIM simulations are used to explain the physical mechanisms of the radiation-induced damage. The devices are promising for radiation-hardened memory applications.

Theoretical studies on distribution of resistances in multilevel bipolar oxide resistive memory by Monte Carlo method

We simulate resistance distributions of multilevel oxide bipolar resistive random access memories (ReRAMs) through a physical model with Monte Carlo method. The model is used to explain frequently noticed proportionality relationship between distributions of resistances and multi-levels program voltages. By comparing with the experimental results obtained with TaOx/Ta2O5 bipolar ReRAM, the model is verified to have a good consistency with experiments not only qualitatively but also quantitatively. We demonstrate that the resistance distributions responses are basically determined by the ion migration barrier in the resistance varying thin oxide layer which means that it is a nearly intrinsic material property.

HfOx bipolar resistive memory with robust endurance using ZrNx as buttom electrode

The high temperature conducting materials Zirconium nitride (ZrNx) films were deposited on silicon-based substrates as bottom electrodes for resistive random access memory (RRAM) cells in Pt (top)/HfOx(x=1.7)/ZrNx (bottom) sandwich structure. The reproducible resistive switching (RS) property of the memory cells was studied systematically for RRAM applications. In contrast to the memory cells in Pt/HfOx/Pt structure, the Pt/HfOx/ZrNx structure show a robust endurance, low and stable operation parameters, large memory window and good retention properties. The composition and chemical bonding states of the prepared HfOx and ZrNx thin films were analyzed by X-ray photoelectron spectroscopy (XPS) technique and the cross-sectional image of the Pt/HfOx/ZrNx structure was observed by high-resolution transmission electron microscopy (HR-TEM). The results show that the formed interface Zirconium oxynitride between the dielectric HfOx film and the ZrNx bottom electrode play key roles in the RS performance improvement.

Multi-level conduction in NiO resistive memory device prepared by solution route

In this paper, we present nickel oxide (NiO) thin film bipolar non-volatile resistive memory device with multi-level conduction prepared by solution route at room temperature. The fabricated device with structure Al/NiO/ITO exhibits excellent switching parameters, such as a stable resistance value in both ON and OFF states for over 10 000 s (retention) and 105 switching cycles of memory operation (endurance). Stable multi-level conductance states are observed in the memory device, which could be exploited for a multilevel-cell programming scheme. The switching mechanism in the resistive memory device is discussed based on the formation/dissolution of conductive filaments.

High Current Density and Nonlinearity Combination of Selection Device Based on TaOx/TiO2/TaOx Structure for One Selector–One Resistor Arrays

We demonstrate a high-performance selection device by utilizing the concept of crested oxide barrier to suppress the sneak current in bipolar resistive memory arrays. Using a TaO(x)/TiO(2)/TaO(x) structure, high current density over 10(7) A cm(-2) and excellent nonlinear characteristics up to 10(4) were successfully demonstrated. On the basis of the defect chemistry and SIMS depth profile result, we found that some Ta atoms gradually diffused into TiO(2) film, and consequently, the energy band of the TiO(2) film was symmetrically bent at the top and bottom TaO(x)/TiO(2) interfaces and modified as a crested oxide barrier. Furthermore, the one selector-one resistor device exhibited significant suppression of the leakage current, indicating excellent selector characteristics.

Modeling for multilevel switching in oxide-based bipolar resistive memory

We report a physical model for multilevel switching in oxide-based bipolar resistive memory (ReRAM). To confirm the validity of the model, we conduct experiments with tantalum-oxide-based ReRAM of which multi-resistance levels are obtained by reset voltage modifications. It is also noticeable that, in addition to multilevel switching capability, the ReRAM exhibits extremely different switching timescales, i.e. of the order of 10−7 s to 100 s, with regard to reset voltages of only a few volts difference which can be well explained by our model. It is demonstrated that with this simple model, multilevel switching behavior in oxide bipolar ReRAM can be described not only qualitatively but also quantitatively.

Resistive switching behavior in diamond-like carbon films grown by pulsed laser deposition for resistance switching random access memory application

In this paper, nonvolatile bipolar resistive memory effects were observed in nitrogen doped diamond-like carbon (DLC) thin films prepared by a pulsed laser deposition technique. It is observed that the fabricated Pt/Ti/DLC/Pt structure exhibits good memory performances with an ON/OFF ratio &amp;gt;10, data retention time &amp;gt;104 s, and low operation voltage (&amp;lt;1.5 V). The current mechanism is fitted by Ohmic and space charge limited conduction laws in low resistance state and high resistance state scenarios. The formation/rupture of metal filaments is due to the diffusion of the titanium ions.

Modulating resistive switching by diluted additive of poly(vinylpyrrolidone) in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)

Here we report a convenient and economic method to modulate resistive switching of a bipolar resistive memory based on Al/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/Al. We found that diluted additive of poly(vinylpyrrolidone) (PVP) in PEDOT:PSS could enlarge the ON/OFF ratio from 103 to 105 and keep a long retention time over 105 s. Besides, the effects of PVP on switching process were studied by detailed analyses of I-V curves, atomic force microscopy images, X-ray photoelectron spectroscopy, and Raman spectra. The enhancement of the resistive window is due to the loss of PEDOT, charge traps, and conformation change induced by PVP.

Excellent Selector Characteristics of Nanoscale $ \hbox{VO}_{2}$ for High-Density Bipolar ReRAM Applications

We herein present a nanoscale vanadium oxide (VO2) device with excellent selector characteristics such as a high on/off ratio (>; 50), fast switching speed ( ; 106 A/cm2). Owing to extrinsic defects, a large-area device with a 20-nm-thick VO2 layer underwent an electrical short. In contrast, after scaling the device active area (<; 5 × 104 nm2), excellent switching uniformity was obtained. This can be explained by the reduced defects and the metal-insulator transition of the whole nanoscale VO2. By integrating a bipolar resistive random access memory device with the VO2 selection device, a significantly improved readout margin was obtained. The VO2 selection device shows good potential for cross-point bipolar resistive memory applications.

A solution processed nonvolatile resistive memory device with Ti/CdSe quantum dot/Ti-TiOx/CdSe quantum dot/indium tin-oxide structure

We report a Ti-TiOx/quantum dot based bipolar nonvolatile resistive memory device. The device has ON/OFF ratio 100 and is reproducible. The memory device showed good retention characteristics under stress and excellent stability even after 100 000 cycles of switching operation. The memory devices are solution processed at room temperature in ambient atmosphere. The operating mechanism is discussed based on charge trapping in quantum dots resulting in Coulomb blockade effect with the metal-oxide layer acting as the barrier to confine the trapped charges. The mechanism is supported by negative differential resistance (NDR) observed exclusively in the ON state.

Oxide Double‐Layer Nanocrossbar for Ultrahigh‐Density Bipolar Resistive Memory

S. H. Chang , S. B. Lee , S. M. ang , Y S. C. Chae , H. K. oo , Y Prof. W Noh . . TReCFI, Department of Physics and Astronomy Seoul National University Seoul 151-747, Korea E-mail: twnoh@snu.ac.kr D. Jeon , . Y S. J. Park , Prof. G. Kim . TSchool of Electrical Engineering Korea University, Seoul 136-701, Korea Prof. B. S. Kang Department of Applied Physics Hanyang University Ansan, Gyeonggi-do 426-791, Korea Dr. M.-J. Lee Semiconductor Device Laboratory Samsung Advanced Institute of Technology Yongin, Gyeonggi-do 446-712, Korea

Effect of the oxygen vacancy gradient in titanium dioxide on the switching direction of bipolar resistive memory

Resistive memory switching behavior depending on voltage sweep direction is studied by intentionally creating oxygen vacancies within titanium dioxide (TiO 2). By inserting a reactive Ti layer on the TiO 2, oxygen deficient TiO 2− x layer is created, which then causes TiO 2− x /TiO 2 which has an oxygen vacancy gradient. This gradient of oxygen vacancy makes it possible to create an insulating TiO 2 layer on the bottom electrode during the first reset with a negative bias at the top electrode. This insulating layer makes counterclockwise directional bipolar switching more stable. On the other hand, under the clockwise directional voltage sweeping, the first set switching is prevented by the insulating TiO 2 layers created during the first and second reset, which leads to a short circuit due to local heating eventually.

Electrical properties and carrier transport mechanisms of nonvolatile memory devices based on randomly oriented ZnO nanowire networks

AbstractWe report reproducible bipolar resistive memory devices based on Au/ZnO nanowire networks (ZnO NWNs)/ITO, which show a high Ron/Roff ratio (∼104) and narrow dispersion of set and reset threshold voltages. The dominant conduction mechanisms of low resistance state and high resistance state were verified by Ohmic behavior and space charge limited current, respectively. The switching mechanism is confirmed in terms of the formation and rupture of conductive filaments, with oxygen vacancies localized on the ZnO NWNs surface involved in. The Au/ZnO NWNs/ITO devices presented in our work show potential applications in the next generation nonvolatile memory field. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

All-inorganic spin-cast quantum dot based bipolar nonvolatile resistive memory

We introduce an all-inorganic solution processed bipolar nonvolatile resistive memory device with quantum dot/metal-metal oxide/quantum dot structure. The two terminal device exhibits excellent switching characteristics with ON/OFF ratio &amp;gt;103. The device maintained its state even after removal of the bias voltage. The switching time is faster than 50 ns. Device did not show degradation after 1-h retention test at 150 °C. The memory functionality was consistent even after multiple cycles of operation and the device is reproducible. The switching mechanism is discussed on the basis of charge trapping in quantum dots with metal oxide serving as the barrier.